Method of producing polyhydric compounds such as ethylene glycol by disproportionation of its monoacetate

ABSTRACT

A polyhydric compound is produced by catalytically disproportionating a precursor which is a lower carboxylate ester of said compound containing at least one lower carboxylate group and at least one free hydroxyl group. Most preferably the invention relates to the production of a diol by the catalytic disproportionation of a lower carboxylate diester of the diol.

Unite States Patent. 1191 Kollar 1 1 Jan. 7, 1975 [5 METHOD OF PRODUCING POLYHYDRIC 3,012,064 12/19 1 Hertling 61; al 260/491 COMPOUNDS SUCH AS ETHYLENE 3,098,093 7/1963 H agemeyer et a1 260/638 R GLYCOL BY DISPROPORTIONATION 0F flmgstag 260/638 R agemeyer et al... 260/638 R ITS MONOACETATE 3,651,102 3/1972 Coopersmithw. 260/635 R 75] Inventor; J Konar, wyckoff" Ni 3,668,239 6/1972 Kollar 260/491 [73] Assignee: Halcon International, Inc., New OTHER PUBLICATIONS York, Horsley et aL, Azeotropic Data," (1952), pages 122] Filed: Sept. 8, 1971 6448190 Lange, Handbook of Chemrstry, 10th ed. (1961), 1 1 nn 178,588 pages 564, 565, TP 151 H25,

[52] U.S. Cl 260/635 R, 203/62, 203/63, Primary Exan 1inerJ0seph E. Evans 203/67, 203/68, 203/69, 203/70, 203/81, Attorney, Agent, or Firm-William C. Long; David 203/82, 203/84, 203/DIG. 6, 260/491, Dick; Riggs T. Stewart 260/621 R, 260/631 R, 260/637 R [51] Int. Cl C07c 31/18, C07c 31/20 57 ABSTRACT [58 Field of Search 260/635 637 638 A polyhydric compound is produced by catalytically d1sproport1onat1ng a precursor WhlCh 1s a lower car- [561 Cited 23230562223031? $5 11?; 12235035 326 11? UNITED STATES PATENTS droiryl group. Most preferably the invention relates to 1,454,60 5/1923 Rodebush 260/635 R the production of a' diol by the catalytic disproportion- 210811322 5/1937 F9 260/633 R ation of a lower carboxylate 'diester of the diol. 2,476,052 7/1949 Llppmcott 260/491 1 2,776,323 1/1957 Toland et a1 260/635 R 3 Claims, 2 Drawing Figures CATALYST I REFINING ESTER FEED LU DISPROPORTIONATION ZONE 1 GLYCOL /4 GLYCOL if. ESTER 1 PATENTEU 5 3,859,368

3F Z4 j 20 CATALYST //Z FE D 25 DISPROPORTIONATION ZONE GLYCOL l GLYCOL+ZX ESTER P I /CARBOXYLIC ACID DSPROPORTIONAT'ION ZONE 70 5i. I I f (77 34 k f 6 I? WATER 50 ga 0N Z LIZO I? 1?? A I /0 Ema HYDROLYSIS ESTER WATER Z E FEED f7, glgllljblfiATlON Z? /4 GLYCOL E2 f 'GLY Z2 [I EST GLYCOL ESTER\ v INVEN'IOR.

JOHN KOLLAR ATTORNEY.

A COMPOUNDS SUCH AS ETHYLENE GLYCOL BY DISPROPORTIONATION OF ITS MONOACETATE This invention relates to the treatment of lower carboxylate esters of polhydric compounds, especially diols and triols, wherein the esters, contain at least one lower carboxylategroup and at least one free hydroxyl group, and is more particularly concerned with the preparation of diols, especially ethylene glycol, by catalytic disproportionation of lower carboxylate monesters of such diols.

Diols and triols are known compounds, many of which are produced commercially in substantial quantities. Thus, etylene glycol, for example, is a chemical of acknowledged commercial importance which is used primarily in the preparation of anti-freeze compositions and in the manufacture of polyester fibers. Ethylene glycol manufacturing processes of commercial interest have generally been based upon the use of ethylene oxide as a raw material. Recently, however, processes have been developed which make it possible to produce diols such as ethylene glycol and propylene glycol v without the necessity for the intermediate manufacture of the oxide. These processes employ the liquid phase reaction of the appropriate olefin, a carboxylic acid,

' and molecular oxygen in the presence of a catalyst to ylate esters produced in such processes. However, the

hydrolysis reaction presents certain problems from the standpoint of efficiency and maximum conversion to the desired glycol. Related problems arise in connection with the production of other polyhydric compounds.

It is an object of this invention to provide an improved process forthe production of a polyhydric compound from a precursor which is a lower carboxylate ester of polyhydric compound and contains at least one lower carboxylate group and at least one free hydroxyl group.

It is another object of the invention to provide a process of the character'indicated which can be combined with the preparation of ethylene glycol by the hydrolysis of lower carboxylate esters of ethylene glycol.

It is an additional object of the invention to provide a process which can be used to produce additional amounts of ethylene glycol from the partial hydrolyzation of lower carboxylate esters of ethylene glycol.

Other objects of the invention will be apparent from the following description of the invention and of illustrative embodiments thereof.

In accordance with the invention, lower carboxylate esters of dihydricand trihydric alcohols, i.e., diols and triols, containing 2 to 6 carbon atoms, which esters contain at least one lower carboxylate ester group and at least one free hydroxyl group, especially lower carboxylate monoesters, are heated in the presence of a catalyst which can be generally characterized as a weak base. It has been discovered that in this environment the lower carboxylate ester undergoes, without the need for the presence of an extraneous reactant, what may be characterized as a disproportionation reaction to produce the free po'lyhydric alcohol, e.g., ethylene glycol, and the corresponding lower carboxylate ester of the polyhydric alcohol which has an added lower carboxylate group, e.g., the lower carboxylate ester of ethylene glycol, as illustrated in the following equations:

2 diol monoester diol diole diester 2 triol monoester triol triol diester 3 triol diester triol 2 triol triester Esters which may be treated in accordance with the invention to produce the corresponding free polyhydric alcohols are the lower carboxylate ester of diols or triols which are hydrocarbon polyols such as the hydroxy derivatives of saturated acyclic or cyclic hydrocarbons or unsaturated acyclic or cyclic hydrocarbons. As indicated, the hydrocarbon radical of such diols or triols may contain 2 to 6 carbon atoms, preferably 2 to 4 carbon atoms in the case of acyclic compounds, and 6 carbon atoms in the case of cyclic compounds. Examples of such esters are the lower carboxylate monoesters of diols such as ethylene glycol, l,2-propane diol (propylene glycol), 1,3-propane diol, 1,4-butane diol, 1,2- butane diol, l,2-cyclohexane diol, 1,4-butene diol, l,2- butene diol, catechol (l,2-benzenediol), resorcinol 1,3-benzenediol), and hydroquinone 1,4- benzenediol), and the lower carboxylate mono-and diesters of triols such as glycerol and 1,2,3-trihydroxy butane.

In the following discussion of the invention, the process will be described and exemplif ed with particular reference to esters of ethylene glycol, especially ethyl ene glycol monoacetate, but the process is equally applicable to esters of other diols and triols as defined above, the discussion in terms of estersof ethylene glyan ester of the alcohol, as disclosed, for example, in

being a monoester in the case of diols, and a monoester or a diester in the case of triols. Accordingly, the lower carboxylate monoesters of ethylene glycol to which the process of this invention is applicable include ethylene glycol monoformate, ethylene glycol monoacetate, ethylene glycol monopropionate, ethylene glycol monobutyrate, ethylene glycol monoisobutyrate, the ethylene glycol monovalerates and the ethylene glycol monocaproates. Ethylene glycol monoformate, ethylene glycol monoacetate, monopropionate, monobutyrate and monoisobutyrate, and mixtures of such monoesters with the corresponding diester, are especially desirable feedstocks, and the monoacetate and the diacetatemonoacetate mixtures are the preferred feedstocks. Of course, mixtures of esters such as mixtures of ethylene glycol monoacetate and ethylene glycol monopropionate, as well as mixtures with one or more diesters, including mixed diester such as ethylene glycol acetate propionate, also can be employed. As used herein, therefore, the term ester feed is intended to include not only the lower carboxylate ethylene glycol monoester alone but also mixtures with the corresponding diester, and mixed esters, as well as mixtures of different ethylene glycol carboxylate esters. In general, mixtures of the monoester with a diester-may contain varying amounts of the corresponding lower carboxylate diester of ethylene glycol, e.g., up to about 85 mol percent of the diester or diesters, based on the combined monoester-diester content of the mixture. Aside from the monoand diesters, small amounts of by-products associated with the preparation of the glycol ester may also be present. Such by-products would normally include small quantities of ethylene glycol itself, water and acids, as well as unreacted lower carboxylic acid. They may also include catalyst residues and aldehydic byproducts, such as, for example, acetaldehyde and formaldehyde. Thus, the effluent from the reaction wherein the monoester is produced can be processed as such in thedisproportionation reaction of this invention. Typical reaction effluents of this nature are described, for example, in the above-mentioned Belgian Pat. No. 738,104, wherein the monoester is produced in the presence of substantial quantities of the diester, andin British Pat. No. 1,124,862, wherein the production of monoester substantially free from diester is disclosed. This invention, however, is applicable to glycol esters produced in any manner, whether by the process of the Belgian patent or the British patent or by various other processes. Further, the ester feed may comprise the effluent from the hydrolysis of ethylene glycol lower carboxylate esters, since even when only lower carboxylate diesters of ethylene glycol are hydrolyzed, the monoesters are formed during the course of the hydrolysis. It is generally preferable to purify such reaction and hydrolysis effluents to remove low-boiling materials, such as water and carboxylic acid, prior to subjecting theglycol ester to. disproportionation. The invention is thus in no way limited to feeds comprising ethylene glycol monoesters from any particular source. In likemanner, the invention is applicable to the corresponding lower carboxylate esters and ester mixtures of other diols and of triols of the character indicated above. i

To provide the catalyst suitable for use in't he disproportionation reaction of the invention there is used a compound which is a weak base in itself,'or a substance which forms a weak base in situ in the presence of ethylene glycol carboxylate esters. For example, there may be used:

a. Metals and metal compounds, such as lithium, so-

dium potassium, calcium, beryllium, magnesium, zinc, cadmium, strontium, aluminum, lead, chrornium, molybdenum, manganese, iron, cobalt, germanium, nickel,-copper, mercury, tin, boron, antimony, bismuth, and cerium as the metal, or an oxide, hydride, carboxylate such as formate or acetate, alcoholate, or glycolate, or metal alkyl, for example tetrabutyl tin, cadmium acetate, lead 'acetate,- zinc acetate, and dibutyl tin diacetate,

b. Tertiary amines, such as trimethyl amine,' triethylcontaining ester in the ester feed to the disproportion-,

ation zone-Preferably, the amount of catalyst is 0.01 to 1.0% and a; particularly preferred quantity is 0.1 to 0.5%. Greater quantities can be used, themaximum amount being generally limited by economic considerations. The catalyst, if desired, can be added directly to the disproportionation zone, but the catalyst is preferably added to the ester-prior to its introduction into the disproportionation zonefThe residence time of the reactants in the disproportionation zone can also vary and, since increased residence times favor increased conversion of theester to the polyhydric compound, a residence time sufficient to effect a reasonable conversion should beemployed, e.g., at least about 0.25,minutes and,-in general, the maximum residence time is governed only by the economics of the system. Preferably, however, a residence time of at least 2 minutes should be employed and, as a general rule, residence times longer than minutes are not particularly useful.

While the disproportionation reaction will take place at ambient temperature, e.g., room temperature, the reaction is favored by heat and it is preferred, there fore, that the reaction be carried out at a temperature of at least about 100C. ln any case, the temperature should beabove the melting points of the polyhydric compound and ester components of the reaction system. Ordinarily, temperatures greater than 280C. are not necessary although higher'temperatures can be employed if desired.

Pressure is not a parameter of the reaction and atmospheric, subatmospheric and superatmospheric pressures may be employed as desired. Obviously minimum and maximum pressure will be related to the type of apparatus available and as a general rule there is not particular advantage in operation at pressure less than 50 mmfig or greater than 250 psig. I

The polyhydric compound thus produced is separated from the reaction mixture in any convenient manner, as by extraction with a selective solvent or by distillation, e.g., extractive distillation or, especially in the case of ethylene glycol and propylene glycol, use may be made of azeotropic'distillation as described in the 1 co-pending application of Richard L. Golden entitled Recovery of Alkylene Glycols. and filed on even date herewith and now US. Pat. No. 3,809,724. In the case of solvent extraction or extractive distillation there is suitably used a high-boiling compound which is inert with respect to the reaction mixture, such as a hydrocarbon or other non-polar or' mildly-polar material such'as an ether. The extracting solvent will be liquid under the prevailing conditions and will most suitably have a boiling point which is 50C. or higher than the boiling point of dica'rboxylate, e.g., ethylene glycol diacetate, in the reaction mixture. A typically suitable hydrocarbon is dodccanc. and a typical extracting ether is diphenyl ether. The disproportionation and the separation ofthe product diol or triol can be carried out individually in different iones but one of the important advantages of this invention is that the disproportionation reaction can be effected simultaneously with the separation operation. Thus, the disproportionation reaction can be effected continuously in a distillation or extraction zone, e.g., a fractional distillation column,

' with continuous introduction of ester feed and continupmum-boiling azeotrope with the polyhydric compound and which can be separated by fractional distillation from any other azeotrope which may be formed, and from other components of the system, and which is essentially water-immiscible, can be used and this embodiment, therefore, is not limited to any particular agent but itis preferred, from the standpoint of ease of operation, to employ an azeotroping agent which forms a mimimum-boiling azeotrope with the polyhydric compound and which has a boiling point at atmospheric pressure of 135 to 190C.? preferably 150 to 170C. When the mixture undergoing disproportionation is concurrently distilled in the presence of azeotroping agents such as agents of the character indicated, the resulting polyhydric compound azeotrope with the azeotroping agent can readily be removed from the system by distillation and the polyhydric compound can be readily recovered. The azeotrope, when condensed, separates into two phases, viz. a phase composed essentially of the azeotroping agent and a phase containing the polyhydric compound. The phase containing the azeotroping agent is readily separated, as by decantation, from the polyhydric compoundcontaining. phase and is returned to the distillation zone, i.e., the zone in which the disproportionation reaction is taking place under distillation conditions, as

reflux. Consequently, the azeotroping agent is merely recirculated in the system and the orginally-supplied quantity of azeotroping agent is continuously available for reuse.

Suitably the azeotroping agent has a boiling point within the above-indicated 135 to 190C. range at atmospheric pressure, most advantageously within the specified preferred temperature range, but it preferably also forms a minimum-boiling azeotrope which has a boiling point which differs by at least 5C. from the boiling point at the same pressure of the azeotropes formed by the polyhydric compound with any of the carboxylate esters of the polyhydric compound present in the mixture. Particularly suitable as azeotroping agents are the saturated hydrocarbons, both acyclic and cyclic, having boiling points within the specified range, the aromatic hydrocarbons, and those which have the required boiling points at atmospheric pressure within the range of 135 to 190C. are, for the most part, alkyl-subsituted benzenes, halogenated hydrocarbons. especially halogenated aromatic hydrocarbons, ethers, ketones and alcohols, and an especially preferred azeotroping agent is pseudocumene. As disclosed in said co-pending application, agents of this character include the following (Table A); wherein the boiling points of the ethylene glycol azeotropes are indicated.

TABLE A Azeotrope Agent b.p.,C. b.p.,C. Azeotroping Agent 760 mm.Hg 760 mm.Hg

Ethylbenzene 133 136.2 Cumene 147 152.8 Anisole 150.5 153.9 Bromobenzne 150.2 156 l-Bromohexane 150.5 156 1,2,3-Trichloropropane 150.8 156.9 Propylbenzene 152 159 o-Chlorotoluene 152.5 159 2,7-Dimethyl Octane 153 160 p-Chlorotoluene 155 162 Mesitylene 156 164.6 1,3-Dibromopropane 160.2 167.3 2,6-Dimethyl-4-Heptanone 164.2 168 Pseudocumene 158 169.5 Phenetole 161.5 172 m-Dichlorobenzene 166 172 2Octanone 168 172.9 Benzylmethyl Ether 159.8 174 Decane 161 174 p Dichlorobenzene 163 174 Heptyl Alcohol 174.1 177 p-Cymene 163.2 177 p-Methylanisole 166.6 177 bis-( 2-ch1oroethyl)ether 171 178 o-Dichlorobenzene 165.8 179 As disclosed in said co-pending application, some typical agents which form minimum boiling azeotropes with propylene glycol include o-xylene (azeo. b.p. 135.8C.), dibutyl eter (azeo. b.p. 136C.) and 2 octanone (azeo. b.p. 169C).

The polyhydric compound containing phase from the azeotropic condensate is subjected to further distillation to remove as overhead the ethylene glycol 'mono carboxylate ester and a relatively small amount of the polyhydric compound, along with any azeotroping agent which may be present, and substantially pure ethylene glycol is withdrawn as bottoms product. the glycol-rich phase from the extractive distillation can be similarly treated. The overhead product from this lastmentioned distillation step is advantageously combined with the feed to the distillation column.

As previously mentioned, the ester disproportionation process of this invention is particularly adapted to be integrated with the hydrolysis of lower carboxylate esters of the polyhydric compound, e.g., ethylene glycol lower carboxylate monoesters, diesters and mixtures of monoesters and diesters, i.e., it can follow the hydrolysis operation in order to produce additional quantities of polyhydric compound. Thus, illustrating the hydrolysis operation by the case of ethylene glycol, which is representative of the other polyhydric compounds within the scope of the invention, not only can the ester feed to the disproportionation reaction consist essentially of ethylene glycol lower carboxylate monoester alone or in admixture with ethylene glycol lower carboxylate diester along with minimum amounts of other materials whichmay be present as a result of the manufacturing process by. means of which the esters are produced but the ester feed may also comprise the effluent from the partial hydrolysis of ethylene glycol carboxylate esters. suitably after removal of water and ester conversion would conventionally require the use oflarge excesses of water. thereby sharply reducing the concentration of the reaction mixture and complicating recovery procedures. It is advantageous, therefore, unless special hydrolysis techniques are employed, to limit the conversion of the ester to about 80 mol i.e., to effect only a partial hydrolysis to this extent. Such hydrolysis can be effected with reasonable quantities of water. The process of this invention makes it possible to increase the ester conversion and thus to produce additional quantities'of ethyleneglycol without problems of increasing conversion in the hydrolysis reaction itself. This. is particularly the case when, in accordance with the preferred embodiment of this invention, the disproportionation is carried out simultaneously 'with az'eotropic distillation. By this means, notonly is removal of the ethylene glycol which is formed as a result of the disproportionation reaction effected, but the ethylene glycol contained in the ester feed to the disproportionation zone is alsoeffectively recovered, so that an integrated system for producing ethylene glycol from its lower carboxylate esters in an efficient manner is provided.

The feed to the hydrolysis operation can be the previously-described ester feed or it can consist essentially of the monoester, or of the diester, or of mixtures of mono-and diesters in any proportion. In general, the

reaction continuesuntil an equilibrium mixture comprising diester, monoester, ethylene glycol, carboxylic acid and water is formed. Before feeding the hydrolysis reaction product to the 'disproportionation reaction, the water and carboxylic acidare preferably removed from the hydrolysis effluent, e.g., by distillation in any convenient manner, these two compounds being readily' separated from the ethylene glycol and the lower carboxylic esters. In effecting the hydrolysis, the ethylene glycol lower carboxylate ester, or ester mixture, is suitably heated in the presence of water until at least some hydrolysishas occurred. Although the hydrolysis reaction will take place solely under the influence of heat, it is preferred, in order to increase the rate of reaction, to effect hydrolysis in the presence of an acidic ester hydrolysis catalyst, most'preferably a solid catalyst, e.g., in the form of an acidic ion exchange resin,'is employed. The hydrolysis step is thus suitably carried out by causing the glycol ester or ester mixture to react under. the influence of heat (with or without a'catalyst) to liberate (i.e., hydrolyze) from 15 to 80 mol of the acyl moieties, e.g., acetate moieties, a lower carboxylic acid, e.g., acetic acid. At the same ti e, ethylene glycol is liberated.

,In the hydrolysis reaction it is desirable to use at least 025 mol of water per equivalent of acyl moiety present in the hydrolysis feed. Preferably the amount of water added is in the range of from about 0.75 to 5 mols of I water per equivalent of acyl moiety in the hydrolysis feed. Of course, greater amounts of water can be used, for'example up to 20 mols per equivalent of acyl moiety in the hydrolysis feed, but the use of such large amounts of water is both unnecessary and econ0mi cally disadvantageous. It is a feature of this invention that the combination of a disproportionation operation with the hydrolysis operation makes it possible to operate the hydrolysis reaction efficiently and effectively by using only limited amounts of'water since only partial hydrolysis is necessary.

Hydrolysis reaction'temperatures of at least about 50C. are necessary in order to obtain economically satisfactory rates of hydrolysis except that, when catalysts are employed, temperatures as low as 25C. can be satisfactorily used. It is-generally not desirable to employ the hydrolysis reaction temperatures above about 25090, however, since at higher temperatures thermal degradation, with concomitant formation of color bodies, can become significant. Prefer-ably temperatures of about 50C. to about 200C. are employed. Pressure is not, in any manner, critical to the conduct of the hydrolysis and the pressure values given above in connection with the disproportionation reaction are suitable as long as they are sufficient at the prevailing temperature to keep the reaction mixture in the liquid phase. Thus pressures of as little as 50 vmrn.l-lg can be employed as also can pressures of several thousand psia. Residence time of reactants and products within the hydrolysis zone is in no way critical as long as the reaction proceeds reasonably near to equilibrium. Thus, for example, residence times from as little as 1 minute up to and including several hours, e.g., 4 hours, or longer are entirely feasible.

While any conventional ester hydrolysis catalyst can be used, for example, materials such as the mineral acids, e.g., hydrochloric, sulfuric and phosphoric'acids, and also include organicacids such as oxalic, tartaric and malic acids, aswell as such materials as trichlora cetic acid and the arylsulfonic acids, e.g., p-toluene sulfonic acid, it is necessary to separate the catalyst from the hydrolysis effluent, e.g., by distilling the rest of the effluent away from the less volatile catalyst, or by chemical treatment to inactivate or remove the hydrolysis catalyst, before further processing. When such catalysts are used, however, they are suitably employed in relatively small amounts, e.g., quantities of as littleas0.000l mol per equivalent of acyl moiety in the feed to the hydrolysis zone being suitable; Larger proportions can be employed though there is little practice reason to employ amounts greater than about 0.001 mol of acid per equivalent of glycol moiety in the feed. It is most preferred, therefore, to u'sesolid catalyst such as acidic ion'exchange resins or molecular sieves, e.g., metal alumina silicates (siliceous zeolites) such as molecular sieves of the A and X series, e.g., Molecular Sieve 4A, and other acidic heterogeneous solid catalysts which can be used in the form of beds through which the feed'to be hydrolyzed can be continuously passed, so that no separation step is necessary. Typical examples of suitable ion exchange resins include catiit is desirable to separate at least 90% of the water and carboxylic acid present in the mixture before proceeding with the removal and recovery of the ethylene glycol. Although, as mentioned, the distillation step to separate water and carboxylic acid can be carried out over a wide range of conditions, it has been found preferaole to operate at pot temperatures of 170 to 240C. and at pressures of from 400 mm. Hg to 50 psig. It will be understood that the water and carboxylic acid can be removed in a single distillation operation or the distillation may be carried out in two distillation zones in series with the water and some of the carboxylic acid being removed in the first distillation zone and the remainder of the carboxylic acid to be removed being separated in the second distillation zone. This distillation step is suitably carried out in conventional manner and the selection of specific conditions for treatment of specific feeds to separate specific amounts of water and carboxylic acid will be readily apparent to persons skilled in the art.

The invention will be more fully understood by reference to the accompanying drawing, wherein:

FIG. 1 is a diagrammatic view of a system for carrying out the disproportionation reaction of the invention simultaneously with removal by distillation of the produced polyhydric compound, illustrated by ethylene glycol, and

FIG. 2 is a similar diagrammatic view of an overall system wherein the disproportionation reaction is integrated with ester hydrolysis, illustrated by ethylene glycol esters.

Referring to the drawing, and more particularly to FIG. 1, an ester feed stream comprising lower earboxylate monoester of ethylene glycol is fed through line to disproportionation zone 12 which, in the embodiment illustrated, is a distillation column suitably provided with heating means, e.g., a conventional reboiler or the like (not shown) and with a bottoms withdrawal line 14 and an overhead vapor line 16, the latter being connected to a condenser 18. The catalyst is introduced through line so that it may be admixed with the ester feed prior to its introduction into the disproportionation zone. The ethylene glycol produced in the disproportionation reaction which takes place in column 12 is removed through line 16, suitably in the form of an azeotrope with an azeotroping agent, and glycol ester is withdrawn through line 14. The overhead vapor from column 12 leaves through line 16 and is condensed in condenser 18, flows to a phase-separator 22, and the condensed azeotroping agent is returned to column 12 through line 24 as reflux, whereas the ethylene glycol phase is withdrawn through line 26 and is introduced into a refining column 28, also provided with any suitable heating means (not shown) wherein ethylene glycol ester and azeotroping agent contained in the ethylene glycol phase withdrawn from phase separator 22 is removed as vapor through line 30, and ethylene glycol in substantially purified form is withdrawn as bottoms through line 32. The vapors in line 30 are condensed in condenser 34 and a portion is returned as reflux to column 28 through line 36 and the remainder is withdrawn through line 38. Some or all of the material in line 38 may be combined with the feed to column 12, and make-up azeotroping agent, as required, is also suitably added through line 10 or through line 20.

Referring now to FIG. 2, wherein the disproportionation-azeotropic distillation system just described is integrated with the hydrolysis of lower earboxylate esters of ethylene glycol to provide the feed to disproportionation column 12, a hydrolysis ester feed stream enters a hydrolysis zone through line 52 and line 54 and water for the hydrolysis enters through line 56 and is combined with the hydrolysis ester feed in line 54 before entering zone 50. Zone 50 is suitably filled with a bed of solid hydrolysis catalyst, e.g., a bed of acidic ion exchange resin, and the combined water and ester feed stream flows upwardly through the bed, and the partially-hydrolyzed reaction product is removed through line 58. The product stream in line 58 is introduced into a water separation column 60, provided with a reboiler or other heating means (not shown) wherein water is vaporized and, along with a small amount of carboxylic acid, is withdrawn through line 62 and condensed in condenser 64. Since in the embodiment illustrated in FIG. 2, the condensate from condenser 64 will contain some azeotroping agent, as will be explained below, the condensate passes to a phase separator 66 wherein the water and carboxylic acid from one phase and the azeotroping agent forms a second phase, the latter being withdrawn from separator 66 though line 68. The aqueous phase is withdrawn through line 70, with part of it being returned to column through line 72 as reflux and the remainder being recycled to column 50 through line 74 which empties into water supply line 56. The portion of the hydrolysis product stream supplied to column 60 which is not vaporized and withdrawn through line 62 and which comprises ethylene glycol, carboxylic acid and lower earboxylate esters of ethylene glycol is withdrawn through line 75 and fed to a distillation column 76, also provided with appropriate heating means (not shown). In distillation column 76, the carboxylic acid is vaporized and carboxylic acid vapors are withdrawn through line 78 and condensed in condenser 80 with some of the condensate being retured to column 76 as reflux through line 82 and the remainder being withdrawn from the system through line 84. The carboxylic acid stream will also contain any water which was not separated in column 60. The essentially water-and carboxylic acid-free ethylene glycol-lower earboxylate ester mixture is withdrawn from distillation zone 76 through line 86 and is supplied to line 10 to provide the. ester feed to disproportionation zone 12, as deseribed'above in connection with the discussion of FIG. 1. To complete the integration of the disproportionation system with the hydrolysis system, a line 90 connects with line 38 to conduct the withdrawn condensate containing azeotroping agent from column 28 to the feed to hydrolysis zone 50 and a side stream from column 12 comprising vapors of lower carboxylate esters of ethylene glycol is withdrawn through line 92 and also combined with the feed to the hydrolysis zone, after being condensed in condenser 88. A purge stream comprising liquid esters and catalyst is withdrawn through line 14 in order to remove the disproportionation catalyst. When the hydrolysis is carried out thermally, i.e., without the use of a hydrolysis catalyst, then the ester stream from the disproportionation zone to the hydrolysis zone can be a liquid stream, e.g., line 92 can be connected to line 14 and the disproportionation catalyst will recycle through the system. Should any of the disproportionation catalyst reach of ion exchange resin serving as hydrolysis catalyst, it will be retained by the resin which can then be suitably regenerated to remove the accummultated disproportionation catalyst or it can be replaced from time to time. Actually, the solid hydrolysis catalyst will eventually become contaminated with minor amounts of impurities which may be contained in the hydrolysis feed and will need to be regenerated in conventional manner, or replaced.

The following examples of specific application will serve to give a fuller understanding of theinvention but it will be understood that these examples are illustrative only and are not intended as limiting the invention.

EXAMPLE 1 A feed mixture composed of 47.2 wt. ethylene glycol diacetate (EGDA),,46.25 wt. ethylene glycol monoacetate (EGMA), 6.4 wt. ethylene glycol (EG), and 0.15 wt. of lead acetate is introducedinto an Oldershaw distillation column consisting of 30 glass trays of 1 inch in diameter above the feed point and 20 trays of 1' inch in diameter below the feed point and provided with a 300 cc electrically-heated glass reboiler powered with a Variac set to maintain a constant temperature of 189C. in the reboiler, and the mixture is distilled in the presence of o-chlorotoluene as azeotroping agent (AA). The overhead vapors (154C.) are condensed in a sloping glass tube condenser, and the condensed two-phase liquid is decanted in a Dean- Stark tube. The heavier liquid comprising ethylene glycol and ester is drawn off-periodically and the lighter liquid comprising the o-chlorotoluene is decanted through the overflow line and is pumped to the top tray of the column at a fixed flow rate.'

During steady state operation 150 cc (approx. 165 g./hr.) of the feed mixture is-introduced at the feed point and 170 cc/hr. of o-chlorotoluene is introduced on the top plate. Most of the AA supplied is reflux of the lighter liquid to which make-up AA is added to compensate for that passing into thewithdrawn overhead phase. Each hour a total of about 31 g. overhead product and a total of about 138 g. of bottoms product are withdrawn from the column. The analyses of each product are as follows, expressed as wt.

Overhead Bottoms EG 72.6 0.67 EGMA 21.8 23.8 EGDA o.1 I 74.1 AA 5.5 [.38

Material balance shows that 49.8% of the EGMA has been converted to E6 and EGDA and that 63.5% of the theoretically attainable EG is in the overhead prod uct. All of the catalyst is in the bottoms product and is excluded from the values given above.

EXAMPLE 11 Overhead Bottoms 150 71.3 0.31 EGMA 22.3 17.0 EGDA 0.l- 82.6 AA 5.72 0.1

Conversion of EGMA to ethylene glycol and EGDA is 60.7% and 73.4% of the theoretical ethylene glycol is in the overhead.

EXAMPLE 111 withdrawn, the analyses of these products, in wt.

being as follows:

Overhead Bottoms EG 87.8 0.37 EGMA 7.75 19.7 EGDA 0.1 79.8 AA 3.25 O.1

Material balance shows that 58%-of the EGMA has been converted to ethylene glcyol and EGDA and that 75.4% of the theoretically attainable ethylene glycol is in the overhead product.

EXAMPLE 1v Using'apparatus corresponding to that described in Example I, but having trays of 2 inch diameter, a feed mixture'having the composition of that used in Example I but containing 0.25 wt. lead-acetate is introduced at the rate of 111 g./hr., and o-chlorotoluene is fed to the top plate at the rate of 130 cc/hr. Each hour atotal of about 20 g. overhead product and a total of about 90 g..bottoms product are withdrawn from the column. The two products analyze as follows in wt.

Overhead o-chlorotolue he Material balance shows that 70.1% of the ethylene glycol monoacetate has been converted to ethylene glycol and EGDA and that 70.4% of the theoretically attainable ethylene glycol is in the overhead product.

EXAMPLE V -Again using the apparatus corresponding to that described in Example I, but having trays of 2 inch diameter, a feed mixture composed of about 46.55 wt. of EGDA, 47.05 wt.-% of EGMA, 6.15 wt. EG and 0.25

wt. lead acetate is introduced at the rate of g./hr., and o-chlorotoluene is fed to the top plate at the rate of cc/hr. Each hour a total of about 31 g. overhead product and a total of about 135 g. bottoms product are withdrawn from the column. The two products analyze as follows, in wt.

Overhead Bmwms portionations are run using various catalysts. In each m 926 '2 case, unless otherwise indicated, the ethylene glycol is IEGMA 2.93 14.9 removed from the disproportionation zone by azeoiiiiDA ii-i 843 tropic distillation with o-chlorotoluene and the compou'chlorololuenc 2.66 01 sition of the feed is 48 wt. EGDA, 46 wt. EGMA, and 6 wt. EG. The pertinent data are shown in Table Material balance shows that 73% of the ethylene glycol B below.

TABLE B Cat. Overhead composition, wt. Bottoms composition, wt. EGMA amt., Iot IIoznl ()vorpercent percent enliven pertemp, Feed, AA, temp., head, sion, l lxmnple Catalyst. ecnt (3. eta/lit. eo./lir. (1. tr./l|r. I') ll ICGMA I'I I DA AA ICU l lt IM A lCtlUA AA percent \"lll. 'lMAA 0. I5 180 I50 105 I51 28 70. 3 L. 2 Ir. 8. *l 1|. 27. l 72. .1 tr. '15 IX ZA 0. 25 186 I50 I05 154 37 57 3 2 Lt. H. 8 0.4 20. l 70. 5 it". 61.0 'l lil 0. 2 101 I50 200 I55 .28 53. 7 35. 8 It. 10. 5 tr. 27. 5 712. 5 LI". 50. 3 'l ll'l 1. 5 100 I50 200 I56 32 58.1] 35. .2 0. 3 5. 6 1.1. 25. 6 74. 1 11'. 54. l

l lJll'lDA 3 187 150 200 I51 32 75. 8 l8. 3 1.1. 5. 8 tr. I6, 5 83. 5 It. 70 l l 1 (1A 0. 15 191 150 10:) 155 34 63. 6 211 1.1. 7. 3 tr. .20. 3 70. 7 t1. 6-1. 0 I\ LA 0.05 189 150 195 151 32 67 26. 3 tr. 6. 7 tr. 23. 4 76. 6 tr. 63. 1 LA 7 0.15 185 150 140 160 34 70. 0 24. 4 ti. 2. 6 11. 15. 1 84. 5 1.1. 58. 2 X\ I.;. LA 0.05 189 150 140 162 2'.) 78. 7 18. 6 tr. 2. 7 tr. 16. J 83. 1 tr. 61. 7

I 1 Mfii=TrinicthyI Ammonium Acetate; ZA=Zinc Acetate; TBT=Tetral utyI Tin; DBTDA=Dibutyl Tin Diacetatc; JA=(3admiuni Acetate;

.11: ea cetate.

*lseudocumcne azeotroping agent; feed comprising (wt. percent) 51.6 E (IDA, 11.6 EGMA, 3.8 EG.

monoacetate has been converted to ethylene glycol and EXAMPLE XVII EGDA and that'84.7% of the theoretically attainable A b' dhd 1 '-d of t' sstem ethylene glycol is in the overhead product. com me y to ysls lsprop r Iona Ion y as illustrated in FIG. 2 is used for continuously hydrolyz- EXAMPLE VI ing an ester mixture containing some ethylene glycol and composed of approximately 54 mol "/1 of ethylene glycol diacetate. 41 mol 7! of ethylene glycol monoacetate, and 5 mol ethylene glycol, and subsequently disproportionating the ethylene glycol monoacetate and recovering ethylene glycol from the system. The following'discussion relates to the operationof this system after steady state conditions are attained.

A feed consisting of ethylene glycol monoacetate containing 0.1 wt. of lead acetate is reacted at 180C. for 15 minutes in a nitrogen atmosphere under a pressure of 100 psig. At the end of this reaction period the product mixture is removed from the reaction zone and contains 5.6 wt. ethylene glycol, 13,1 wt.

% ethyienetgiycoi diacetaie and ethylene The fresh feed mixture is introduced through line 56 giycoi moiioaceiawr at a rate to provide, per hour, 244.7 lb. mols EGDA, when either. ethylene glycol or ethylene glycol dlacfi- 184.9 lb. mols EGMA, and 24.4 lb. mols EG, and this i is removed imm the mixture as by Soivem exirac' mixture is combined with recycle streams 90 and 92 to tion or distillation, the remaining mixture is further reprovide a flow of approximately 1,088 m01S/hr acted, additional amounts of ethylene glycol and ethyl- 4O EGDA and 185 mols/hr. EGMA, 343 1 e ne glycol diacetate are formed by further dispropormols/hr. EGy into hydrolysis Zone 50, which is main iionaiioii of the eihyiene giywi monoacetate tained at a temperature of 90C. and consists of about an 800 cubic foot bed of 100 to 200 mesh Dowex EXAMPLE VII 50W-X8 ion exchange resin. At the same time water is A feed consisting of 208 g. ethylene glycol monoaceintroduced at the rate of approximately 656.4 lb.

tate containing 0.25 wt. zinc acetate, is introduced mol /hr, make up water and approximately 530.9 lb. near the top of a countercurrent extraction column mol /hr, recycle watercontaining a small amount'of having 20 extraction stages and maintained at a temacetic acid, The partially-hydrolyzed product (about perature of 180C. The feed is passed downwardly 52% of the EGDA fed to the hydrolysis zone remains countercurrently to 600 g. of hexadecane introduced at unconverted) i ithd w th h lin 58 and passed the bottom of the column and the flow is at a rate to to h 9 plate f the top of column 0 which provide an average res fl e o 8190111 5 minutes tains 53 actual plates and is operated at a reboiler temper stage. The hexadecane phase which is removed perature of about 152C. and at substantially atmofrom the top of the apparatus is composed of approxispheric pressure, with a reflux ratio of 2:1 to separate maieiy 600 gheXadeCahe and i30 eihyiehe g Y 55 as overhead the water-acetic acid recycle stream and a diaceiaie, Whereas iheieihyiehe glycol Phase removed bottoms stream comprising the remainder of the hydrofrom ihe bottom of ihe apparatusiamoiihis i078 gand lysis effluent which is passed onto the 12th plate from is composed of eihyiehe g y and the top'of column 76 which has 28 actual plates and is eihyiehe giycoi mohoaceiaieoperated at a reboiler temperature of 182C. and at at- Whfih the Processes of the foregoing examples are mospheric pressure, with a reflux ratio of 1.6:1. Azeorepeated with Corresponding amounts of irimeihyi troping agent in recycle stream 90 is removed in sepamohiiim t Zinc acetate, (lead acetate in the case rator 66 and returned to column 12 through line 68. In of Exampie Vii) ieiiabiiiyi dihiiiyi diaceiaie, column 76 the remainder of the acetic acid and water Cadmium acetate, or irimeihyi ammonium amine as are separated and withdrawn through line 84. The botdispioporiiohaiioh caiaiysi Corresponding dispropoi' toms product from column 76, comprising the ester iiohaiioh of the mohoesier is achieved and glycol components of the hydrolysis reaction, has added to it lead acetate at the rate of approximately EXAMPLES VIII XVI 0.24 lb. mol/hr. and the mixture is introduced to the Using the apparatus of Example I, a series of dispro- 20th plate from the top of the azeotropic distillation column 12 which contains 55 actual plates and employs o-chlorotoluene as azeotroping agent which is continuously recycled to the column through lines 24 and 68 and is present in an amount to provide a ratio of azeotroping agent to ester-glycol feed of approximately 1.9: 1. All of the azeotroping agent condensed and separated in separator 22 is returned to column 12 and the ethylene glycol phase from separator 22, which contains approximately 4 mol o-chlorotoluene, 19 mol EGMA, and is free from EGDA, is fed to refining column 28 which contains 60 actual plates and isoperated at a reboiler temperature of'173C'. and at a pressure of 200 -mm.Hg with a refluxratio of 7:1 and there is obtained a bottoms product consisting essentially of ethylene glycol, which is withdrawn at the rate of approximately 444 lb. mols/hr, and the net overhead, as .previously mentioned, is recycled to the hydrolyzer through line'90. An ester purge stream of 9 lb. mols/hr.

' (calculated as ethylene glycol diacetate) and containing the catalyst is withdrawn through line 14 and can be processed for-catalyst recovery, ifdesired and the catalyst recycled to line 20. A vapor stream composed substantially entirely of EGDA is withdrawn through line-92 from above the 53rd plate 'from'the .top of column l2 and, after condensation in condenser 88 providcs the previously-mentioned recylc stream. In the foregoing example there was substantially 85-90% conversion of EGMA to E6 and EGDA. 7

1n the foregoing example, the hydrolysis feed contains ethylene glycol and a substantial amount of ethylene glycol monoester which is representative of a feed which would normally be available from the processing of a carboxylate ester product produced by the reaction of acetic acid and ethylene, but corresponding effective operation is also realized when'this example is repeated with afeed containing essentially no ethylene glycolor lesser amounts of ethylene glycol monoacetate or composed essentially of ethylene glycol diacetate. Such feeds require appropriate adjustment in the operation of the distillation units as will be obvious to persons skilled in the art. Ethylene glycol which is recovered as the product of this process is of high-purity such that it can be used directly in the production of fiber-grade polyesters.

What has been said above with regard to the treatment of lower carboxylate esters of ethylene glycol and with respect to the production and recovery of ethylene glycol also applies, as previously indicated, to the treatment of lower carboxylate esters of other polyhydric compounds of the character specified above. Thus,

when Example V1, for instance, is repeated using propylene glycol monoacetate, or the monoacetate of 1,4-

butane diol, or the monoacetate of 1,2-butene diol, or the monoacetate of catechol, or the diacetate of glycerol, corresponding results are achieved and effective production of the free polyhydric compound is realized. In like manner, corresponding results are obtained when the esters of other lower alkanoic acids are used in place-of the acetic acid esters, for example the formates and propionates. It is intended, therefore, that all matter-contained in the foregoing description shall be interpreted as illustrative only and not as limitative of the invention.

Iclaim:

1.-A process for producing ethylene glycol or propylene glycol from a feed comprising an ester which is the monoformate, the monoacetate or the monopropionate of said glycol which comprises the steps of:

a. introducing said feed into a reaction zone,

b. reacting said feed in said reaction zone at a temperature within the range of room temperature up to about 280C. with a residence time of 0.25 to 50 m'inutesin the presence of a basic disproportionation catalyst which is a weak base or a substance which forms a weak base in situ in'the presence of said ester, said catalyst being employed in the amount of 0.001 to 5 by weight based upon said ester in the feed to convert at least some of said ester to ethyleneglycol and to ethylene glycol-diester or to propylene glycol and to propylene glycol diester, and

c. concurrently recovering said thus-produced ethylene glycol or propylene glycol from said reaction zone by separating it from said feed ester and said produced ester by azeotropic distillation wherein an azeotr ope of said ethylene glycol or propylene glycol is removed as overhead distillate.

2. A process as defined in claim 1, wherein said cataacetate, lead acetate or zinc acetate. 

1. A PROCESS FOR PRODUCING ETHYLENE GLYCOL OR PROPYLENE GLYCOL FROM A FEED COMPRISING AN ESTER WHICH IS THE MONOFORMATE, THE MONOACTATEOR THE MONOPROPIONATE OF SAID GLYCOL WHICH COMPRISES THE STEPS OF: A. INTRODUCING SAID FEED INTO A REACTION ZONE, B. REACTING SAID FEED IN SAID REACTION ZONE AT A TEMPERATURE WITHIN THE RANGE OF ROOM TEMPERATURE UP TO ABOUT 280*C WITH A RESIDENCE TIME OF 0.25 TO 50 MINUTES IN THE PRESENCE OF A BASIC DISPROPORTIONATION CATALYST WHICH IS A WEAK BASE OR A SUBSTANCE WHICH FORMS A WEAK BASE IN SITU IN THE PRESENCE OF SAID ESTER, SAID CATALYST BEING EMPLOYED IN THE AMOUNT OF 0.001 TO 5 % BY WEIGHT BASED UPON SAID ESTER IN THE FEED TO CONVERT AT LEAST SOME OF SAID ESTER TO ETHYLENE GLYCOL AND TO ETHYLENE GLYCOL DIESTER OR TO PROPYLENE GLYCOL AND TO PROPYLENE GLYCOL DIESTER, AND C. CONCURRENTLY RECOVERING SAID THUS-PRODUCED ETHYLENE GLYCOL OR PROPYLENE GLYCOL FROM SAID REACTION ZONE BY SEPERATING IT FROM SAID FEED ESTER AND SAID PRODUCED ESTER BY AZEOTROPIC DISTILLATION WHEREIN AN AZEOTROPE OF SAID ETHYLENE GLYCOL OR PROPYLENE GLYCOL IS REMOVED AS OVERHEAD DISTILATE.
 2. A process as defined in claim 1, wherein said catalyst is a metal carboxylate.
 3. A process for producing ethylene glycol or propylene glycol as defined in claim 1, wherein said catalyst is cadmium acetate, lead acetate or zinc acetate. 